JP6116553B2 - Method and apparatus for measuring liquid flow rate - Google Patents

Description

  The present invention relates to the field of flow meters. In particular, the present invention relates to a flow meter that can accurately determine the volume flow rate of a liquid.

  Flow measurement is important in many fields. For example, many industrial processes require measuring flow rates through various conduits in order to properly control the process. Other applications that require measuring liquids or gases include delivering products such as gas, oil, and water to consumers.

  In the medical field, liquid measurement may be applied to urine output of a subject or intravenous administration of a drug. Acute kidney injury (AKI) is a common problem for hospital patients, especially in critical care and operating rooms. However, it is only recently that medical has found conditions for assessing and classifying AKI risk and progression. These conditions identify five major stages in the progression of AKI. Risk, Injury, Failure, Failure of Renal Function (Loss), End Stage Renal Disease (known as the RIFLE classification for these initials) It is. Based on the success of RIFLE, an acute renal failure network (AKIN) was formed by an international expert group of advanced physicians addressing the AKI problem. AKIN supports and promotes RIFLE. They also proposed a modified version of RIFLE called the AKIN classification. The RIFLE-AKIN classification provides a useful tool to suppress AKI. These classifications include measuring creatinine clearance and urine output. Creatinine clearance is a very late indicator that only indicates that AKI has already occurred. Urine output as a result of measuring renal function is usually assessed on a daily basis or a time shift (eg every 8 hours) basis.

  The heat transfer flow meter continuously measures the flow rate using a heating element and two temperature sensors (upstream and downstream of the heater or adjacent to the heater). By measuring the temperature difference between the two thermometers, the flow rate is calculated. Alternatively, the flow rate can be calculated by maintaining the temperature at a constant value equal to or higher than the ambient temperature of the liquid in the heater and monitoring the energy required for this.

  FIG. 1 schematically shows the basic arrangement of a heat quantity flow meter in the prior art. The liquid flows through the tube 100 in the direction indicated by the arrow. A heating element 120 is placed either in the side wall of the tube or in the tube. The temperature sensor 110 measures the temperature Ti, the temperature sensor 112 measures the temperature Tj, and these sensors are arranged upstream and downstream of the heater 120, respectively. The isotherms 130, 131, 132 show the temperature distribution obtained as a result of the power input to the heating element. T130> T131> T132.

The calculation to determine the flow rate is made by the following formula:

The symbols used in the above formula are defined in the following table:

  Related types of heat transfer flow meters, particularly those known as constant temperature flow meters, use a configuration similar to FIG. However, the temperature sensor 112 is adjacent to or integrated with the heating element 120. In this configuration, the heating element 120 is heated to a specified fixed differential temperature Tj (measured by the sensor 112) equal to or higher than the temperature Ti measured by the sensor 110. The amount of heat carried away by the fluid depends on the flow rate. The temperature of the heater 120 is kept constant by adjusting the applied current. As shown in Equation 3, the flow rate can be calculated from the current value (I) necessary to maintain the fixed temperature difference ΔT.

  In the basic configuration of the above-described conventional heat quantity flow meter, heat is applied to the liquid by the heating element 120 until the temperature reaches Tj. At this point, the heating element is turned off and the time for the temperature to return to the original value Ti is measured. Although the time of the first measurement point is known accurately, it is difficult to determine the exact time at which the second measurement should be performed. This is because the temperature changes relatively slowly as it approaches a stable value. Also, when the flow rate is measured repeatedly, the ambient temperature of the liquid rises slowly, so that an accurate value for the liquid Ti cannot be obtained. Furthermore, since the conventional calorific flow meter needs to continuously supply energy to the heating element, it is not energy efficient to use it.

  Accordingly, an object of the present invention is to provide a method for determining the flow rate of liquid easily and accurately.

  Another object of the present invention is to provide a simple, cost effective and accurate flow meter.

  Another object of the present invention is to provide a flow meter with low energy requirements.

  Other objects and advantages of the present invention will become apparent from the following description.

The first aspect of the present invention is an apparatus for measuring the volume flow rate of a liquid flowing through a conduit. The apparatus comprises the following configuration:
a) a heating element in thermal contact with the liquid in the conduit, the heating element configured to supply a known amount of heat to the flowing liquid;
b) a temperature sensor configured to measure the instantaneous temperature of the heating element;
c) A control system including at least one of a processor, an input unit, a memory unit, a display device, and an output unit, wherein each component of the control system is configured as follows. ;
i) operating the heating element to supply the known amount of heat;
ii) receiving a measurement result of the instantaneous temperature of the heating element from the temperature sensor;
iii) obtaining calibration data stored in advance in the memory unit and relating the temperature change of the heating element and the known flow rate of the liquid;
iv) The volume flow rate is determined using the known heat quantity, the measurement result of the instantaneous temperature of the heating element, and the calibration data stored in advance.

In the apparatus embodiment, the components of the control system are configured to implement at least one of the following:
a) storing and displaying to the user information relating to the operation of the device and information relating to the properties of the liquid measured or determined by components of the device;
b) sending an instantaneous or historical value of the measured temperature and other information about the liquid and the device to a remote location;
c) send a signal that can be used as an input to another system;
d) Send a warning if there is a predetermined change in the flow rate or other measured property of the liquid.

Embodiments of the apparatus comprise at least any of the following:
a) a bubble trap placed upstream of the measurement point;
b) A gas permeable thin film disposed upstream of the measurement location.

  The device can be connected to or configured as part of the conduit. In an embodiment of the device, the conduit is a catheter or drain tube leading from the subject. The control system of the device can be configured to detect the risk of acute renal failure and its stage.

The second aspect of the present invention is a method for measuring in real time the volumetric flow rate of liquid flowing through a conduit. A heating element configured to thermally contact the flowing liquid and to supply a known amount of heat to the flowing liquid; a temperature sensor configured to measure an instantaneous temperature of the heating element; A control system having a processor and a memory unit is used. The method has the following steps:
i) measuring the temperature Ti of the heating element;
ii) operating the heating element to supply a known amount of heat to the flowing liquid;
iii) measuring the temperature Tj of the heating element immediately after supplying the known amount of heat to the flowing liquid;
iv) determining a value of ΔT = Tj−Ti from the measurement result;
v) Recalling a calibration table, graph, or mathematical relationship constructed for the known heat quantity from memory and determining the flow rate corresponding to the measured ΔT value from the calibration table, graph, or mathematical relationship. .

  An embodiment of the method according to the invention is configured to measure the volumetric flow rate of the liquid via a catheter or drain tube leading from the subject. The flowing liquid may be urine. In an embodiment of the method wherein the flowing liquid is urine, the measurement result can be used to detect the risk of acute renal failure and its stage.

Another aspect of the present invention is a heating element that is in thermal contact with a liquid flowing through a conduit and configured to supply a known amount of heat to the flowing liquid, and to measure the instantaneous temperature of the heating element. A calibration table, graph, or mathematical relationship that can be used to determine a value of the flow rate that corresponds to a known calorimetric measurement ΔT supplied by the heating element using a temperature sensor configured to Is a way to build. The method has the following steps:
a) adjusting the flow rate to a known fixed value;
b) measuring the temperature Ti of the heating element;
c) operating the heating element to supply the known amount of heat to the flowing liquid;
d) measuring the temperature Tj of the heating element immediately after the known amount of heat is supplied to the flowing liquid;
e) determining ΔT = Tj−Ti;
f) storing the value of the flow rate, the amount of heat, and ΔT in a memory unit;
g) repeating steps a to f for known values of a plurality of flow rates.

  These and other features and advantages of the present invention will be readily apparent by reference to the following examples and accompanying drawings.

The basic composition of the heat transfer flow meter in a prior art is shown roughly. 1 schematically shows a cross-section of a conduit with components used to measure the flow rate of liquid passing therethrough, according to an embodiment of the invention. 1 schematically shows a single heating pulse applied to the device and the corresponding temperature change versus time graph; 1 schematically shows a single heating pulse applied to the device and the corresponding temperature change versus time graph; 1 schematically shows a single heating pulse applied to the device and the corresponding temperature change versus time graph; 3 schematically shows three successive heating pulses and the corresponding temperature change versus time. Figure 3 schematically shows a graph of power and temperature change integration versus time applied to the device. 1 schematically illustrates a system for measuring urine flow from a subject with a catheter inserted, according to one embodiment of the present invention.

  The present invention relates to a method and apparatus for measuring the flow rate of liquid flowing through a conduit. The device is based on a flow meter configured to accurately measure the volumetric flow rate of a liquid in a simple, cost effective and energy efficient manner and with an accurate method using only one temperature sensor. The method is based on applying a pulse of thermal energy to the flowing liquid and measuring the temperature rise as a function of time and energy input. The flow rate can be determined by comparing these measurement results with a calibration table created by performing a similar measurement for a known flow rate. One application is to measure the flow of urine excreted by a subject who has inserted a catheter, which will be described below to illustrate the features of the method and apparatus according to the present invention.

  FIG. 2 schematically illustrates a cross-section of a conduit 200 (eg, a tube, catheter, or pipe) that includes components used to measure the calorimetric flow of liquid passing in the direction indicated by the arrow. The heating element 220 is disposed in the conduit 200 and is inserted directly into the flowing liquid. In other embodiments, element 220 is disposed on the heat conducting portion of the conduit wall. By applying a voltage via the lead 221, electric power is supplied to the heating element 220. The temperature sensor 212 is adjacent to or integrated with the heating element 220. The temperature sensor 212 measures the temperature of the heating element 220. The temperature measured by the sensor 212 is read out via the lead 213. In order to minimize heat loss, it is desirable that the cross section of the conduit including the heating element 220 and the temperature sensor 212 be thermally isolated from the surroundings using an optional insulating member 230.

  A plurality of heat sources can be used as the heating element 220. Possible heating elements 220 are, for example, an electrical resistance and a thermistor or a suitably configured metering heat exchanger. Measuring the energy input and applying it to the heating element 220 is accomplished by techniques well known in the art depending on the heat source used.

  Thermal sensors that can be used in the flow meter of the present invention include, for example, transistors, thermocouples, thermistors, thermocouple arrays, and other types of thermal sensors that are now known or future known in the art.

  The heating element and the temperature sensor are shown as separate elements for convenience in explaining these functions. However, embodiments are possible that allow both heating and temperature measurement using a single element, such as a self-heating thermistor or a resistance thermal device (RTD).

  Depending on the application, it is necessary to ensure that bubbles that affect the measurement accuracy are removed from the liquid measurement location. To achieve this, one or more bubble traps can be employed upstream of the measurement location. As an alternative or in combination with a bubble trap, a ventilation means can be arranged upstream of the measuring point, for example a gas permeable membrane that allows gas to be discharged from the conduit.

  Depending on the direction and flow rate of the conduit, the conduit or part of it may not be filled with liquid at the measurement site. Therefore, depending on the application, a check valve should be installed downstream of the measurement point to generate enough back pressure to fully fill the conduit at the measurement point.

  Leads 213 and 221 are connected to the control system. The control system is configured to operate the heating element a predetermined number of times, receive data from a temperature sensor and a device that measures energy input to the heating element, such as an ammeter, and use this data to determine the flow rate. An electric circuit or a processor. The control system also includes input means such as keypads, keyboards, buttons, switches, touch screens, touchpads, trackballs, mice and other pointing devices, so that the user can be lengthy and / or applied It is possible to control parameters such as the amount of heat energy and the measurement period. The control system also includes one or more memory units, a display unit, and output means for storing and presenting system parameters to the user. The output means comprises a communication device configured to transmit instantaneous data or historical data to a remote location using wired or wireless technology. The control system can also be configured to use the output means to transmit a signal that provides input to another system. For example, in a hospital facility, the control system sends a warning to the nurse station when the urine flow from the catheterized subject to the collection bag falls below a predetermined amount, or when an abnormal flow occurs in the intravenously administered drug. An alert can be configured to be sent. In the case of urine measurement, the control system can be configured to use the measurement results to provide a current real-time assessment of renal function and an early warning of the situation related to AKI.

As with the prior art, the flow rate can be determined using the following formula:

In the method according to the invention, it is assumed that for a given liquid, ρ and Cp representing the liquid properties are constant and are defined as follows:

Thus, for a given time period, the temperature change (ΔT) is a function of flow rate (or vice versa), with one Q increasing and the other decreasing when Q is constant. For example, as the flow rate increases, more heat is carried away from the heating element and ΔT (ie, the degree to which the heating element is at a higher temperature compared to the unheated (ambient) state) becomes smaller. Conversely, when the flow rate is reduced, the amount of heat removed from the heating element is reduced, and ΔT is increased.

  An embodiment of the method according to the invention is shown in FIGS. 2 and 3A. The temperature of the heating element 220 is first measured by the temperature sensor 212. This measurement is shown as Ti in the rising curve (temperature vs. time) in FIG. 3A. Following the measurement of the temperature Ti, known or measured energy is applied to the heating element 220 in a manner suitable for the heat source. Finally, at time t2 immediately after the energy application is completed, the temperature Tj of the heating element is measured.

Energy can be applied to the heating element 220 in various ways. For example, electrical energy can be applied to the resistance heating element by any of the following methods:
a) Applying a specified power level (eg watts) over a specified period (eg 1W for 60 seconds or 50mW for 10 seconds) depending on the heating element and temperature sensor used;
b) discharging the charged capacitor circuit from a given first voltage level to a given second voltage level;
c) Using a coil boost circuit with transistors, supply a series of measured currents “micropulses” that, when connected, result in a specific “macropulse”.

  FIG. 3A shows a measurement result of one period substantially. In this example, the power curve (lower curve showing power versus time) shows that a rectangular heating power pulse is applied from time t1 corresponding to temperature T1 to time t2 corresponding to temperature T2. As a result, the upper temperature change detection curve is obtained. In this case, the temperature change is measured over the entire duration of the pulse. That is, ΔT = T2−T1 = Tj−Ti.

  The temperature measurement to determine ΔT need not necessarily be linked to the duration of the heating pulse. For example, as shown in FIG. 3B, Ti may be measured after time t1, and Tj may be measured before time t2.

  The heating pulse is not necessarily rectangular as shown in FIGS. 3A and 3B. The pulses can be delivered in different ways and can have different waveforms. For example, as shown in FIG. 3C, it may be a capacitor discharge pulse curve.

  3A-3C illustrate two important features of the present invention. Initially, as can be seen from the temperature vs. time graph, after the heating pulse is applied, i.e. starting from time t2, the liquid passing through the heating element returns to approximately the first temperature value at time t3. It takes a long time. In the prior art, it is necessary to wait until the temperature returns to a slightly different range from the original (ambient) temperature before a new measurement can be performed. There are also situations where the ambient temperature naturally changes. For example, for the body fluid, the body temperature of the subject naturally changes, and the temperature of the discharged body fluid (for example, urine) also changes accordingly. Similarly, the ambient temperature of the environment may change, which affects the liquid temperature. In such a situation, without another reference temperature sensor, it cannot be determined whether or not the temperature measurement result reflects the current ambient temperature of the liquid.

  In the present invention, it is not necessary to wait until time t3 and then apply the next heating pulse to start the next measurement cycle. Furthermore, the starting temperature of the first measurement need not be the same as the starting temperature of the second measurement. This is shown in FIG. The figure shows a series of successive heating pulses.

To determine the flow rate using Equation 6 , a series of measurements is performed. For a given value Q, the value of ΔT is determined by the apparatus according to the invention for various known flow rates. As a result, a data table for mapping the flow rate and ΔT (or a point set representing a heating change curve) obtained experimentally is obtained. The calibration data is specific to the conduit, the liquid in the conduit, the parts of the device according to the invention, and the value of Q. Due to the manner of acquisition, the calibration data also takes into account heat losses to the conduit and the environment. Using the acquired table, the mathematical relationship can be determined in the form of a mathematical expression. A calibration table or graph (or a set of tables and graphs for each different Q value) is stored in the memory of the processor of the control system. These can be obtained from the memory and the flow rate can be automatically determined from the measured value of ΔT.

  The measurement frequency depends on the characteristics of the fluid to be measured. For example, whether the flow rate is expected to be constant or change rapidly. It also relies on significant changes in flow rate. In this case, it is important to know the change as soon as possible. In one embodiment, the measurement frequency is determined by the operator of the device. For example, once per hour. In other embodiments of the invention, the frequency of the measurement cycle is a function of the expected or actual rate of change of the flow rate. Thus, for example, more measurements are performed during the day when the change in flow is expected to be relatively large, and fewer measurements are performed during the night when the change in flow is expected to be relatively small.

  The measurement timing can also be automatically determined by the control system. In one embodiment, after the heating pulse is applied, the control system is programmed to detect when the liquid temperature returns to a stable value. When the control system detects a return to a stable state, the control system activates the heating element again and starts a new measurement cycle. In other embodiments, the control system can determine measurement timing based on flow rate changes during a specified number of previous measurements.

  The amount of energy that must be supplied to the heating element depends on the properties and flow rate of the liquid. The appropriate energy value within the pulse can be determined experimentally for a given application. When the flow rate is large, the applied heating energy may be increased to improve the signal to noise ratio. In an embodiment of the present invention, the processor of the control system automatically adjusts the amount of energy delivered based on the flow rate measured in the most recent heating pulse or based on the average flow rate or trend estimate measured in multiple previous pulses. It can be constituted as follows. Alternatively, this can be performed when pre-measurement is insufficient (ie ΔT is below a certain value) or heating is excessive (ie ΔT is above a certain value).

  In the embodiment of the invention shown in FIG. 5, the temperature is measured multiple times during the heating pulse, thereby obtaining a set of data points representing a temperature rise curve. The integral value of the curve obtained between the times t1 and t2 can be used as a flow rate measurement result. For a given value Q in the pulse, this integral is assumed to decrease as the flow rate increases. This is because as the flow rate increases, more heat is lost and the temperature curve does not rise as when the flow rate is low. As a result, the region under the temperature curve between times t1 and t2 becomes smaller. Similar to other embodiments, a calibration measurement can be performed using a known flow rate, and a lookup table can be constructed that associates the integral measurement with the unknown flow rate.

  The sensor part of the device according to the invention, ie the heating element and the temperature sensor, can be “built in” according to specific streamlines. Alternatively, it can be provided as an individual unit that can be attached to an existing streamline. For example, to measure urine flow, the unit can be equipped with a standard connector, one connected to the catheter and the other connected to the drain tube or collection bag. In other embodiments, it can be incorporated as an integral part of the catheter or drain tube.

  FIG. 6 schematically illustrates an embodiment of a system 400 for measuring urine flow from a catheterized subject (not shown). A catheter 410, sensor section 414 (detailed in FIG. 2), drain tube 418, collection bag 420, and control system 430 are shown. Bubble trap 412 is an optional part of system 400.

  While embodiments of the invention have been described for purposes of illustration, it will be appreciated that various changes, modifications and applications of the invention may be made without departing from the scope of the claims.

Claims (12)

A device for measuring the volumetric flow rate of a liquid flowing through a conduit,
a) a heating element in thermal contact with the liquid in the conduit, the heating element configured to supply a known amount of heat to the flowing liquid for a known period of time;
b) a temperature sensor configured to measure the instantaneous temperature of the heating element;
c) a control system including at least one of a processor, an input means, a memory unit, a display device, and an output means;
With
i) The processor of the control system is configured to operate the heating element from time t1 until time t2 ends;
ii) The processor of the control system is configured to receive from the temperature sensor an initial measurement result Ti of the instantaneous temperature of the heating element and a final measurement result Tj of the instantaneous temperature, where Tj is a known period Measured after Ti is measured;
iii) The memory of the control system stores a pre-built calibration table, graph, or mathematical relationship, the configuration table, graph, or mathematical relationship at a known period for the liquid Can be used to determine a volumetric flow rate corresponding to a measured change in temperature of the liquid for a known amount of heat supplied;
The device, together configured to measure Ti after time t1, apparatus characterized by being configured to measure Tj prior to time t2. The components of the control system are configured to perform at least one of the following:
a) The memory portion and the display device of the control system store and display information relating to the operation of the device and information relating to the properties of the liquid measured or determined by components of the device to the user. Composed of;
b) the output means of the control system is configured to transmit instantaneous or historical values of measured temperature and other information about the liquid and the device to a remote location;
c) the output means of the control system is configured to transmit a signal that can be used as an input to another system;
d) the output means of the control system is configured to send a warning if there is a predetermined change in the flow rate or other measured property of the liquid;
The apparatus according to claim 1. The apparatus comprises at least one of the following:
a) a bubble trap placed upstream of the measurement point;
b) a gas permeable thin film disposed upstream of the measurement location;
The apparatus according to claim 1. The apparatus of claim 1, wherein the apparatus is connected to or configured as part of the conduit. The apparatus according to claim 4, wherein the conduit is a catheter or a drain tube communicating with a subject.   6. The processor of claim 5, wherein the processor of the control system is configured to provide a current real-time assessment of renal function and an early warning of a situation related to AKI using measurement results of urine flow. apparatus. A method for measuring a volumetric flow rate of a liquid flowing in a conduit in real time, the method being in thermal contact with the flowing liquid and configured to supply a known amount of heat to the flowing liquid for a known period of time. Using an apparatus comprising: a heating element; a temperature sensor configured to measure an instantaneous temperature of the heating element; a control system having a processor and a memory unit;
i) operating the heating element starting at time t1 and ending at time t2;
ii) measuring the temperature Ti of the heating element;
iii) measuring the temperature Tj of the heating element in a known period after the temperature Ti is measured;
iv) Calling a calibration table, graph, or mathematical relationship constructed for the known amount of heat from the memory unit, and the flow rate corresponding to the measured Tj-Ti value from the calibration table, graph, or mathematical relationship Determining
Have
Ti is measured after the time t1,
Tj, a method characterized in that it is measured before the time t2. The method of claim 7, wherein the method is configured to measure the volumetric flow rate of the liquid via a catheter or drain tube leading from a subject.   The method of claim 8, wherein the liquid is urine. The method according to claim 9, wherein a risk of acute renal failure and a stage thereof are detected using a result of the measurement. A heating element that is in thermal contact with the liquid flowing through the conduit and is configured to supply a known amount of heat to the flowing liquid for a known period of time, and is configured to measure the instantaneous temperature of the heating element. And using the temperature sensor to determine a value of the flow rate corresponding to a measured value of the temperature change of the liquid for a known amount of heat supplied to the liquid in a known period by the heating element. A method of building a calibration table, graph, or mathematical relationship that can be:
a) adjusting the flow rate to a known fixed value;
b) operating the heating element starting at time t1 and ending at time t2;
c) measuring the temperature Ti of the heating element;
d) measuring the temperature Tj of the heating element in a known period after the temperature Ti is measured;
e) storing the value of the flow rate, the value of the amount of heat supplied to the liquid in a known period between the measurement of Ti and Tj, and the value of Tj-Ti in a memory unit;
f) repeating steps a to e for known values of a plurality of flow rates;
Have
Ti is measured after the time t1, method characterized in that Tj is measured before time t2. A method for measuring the volumetric flow rate of a liquid flowing through a conduit using an apparatus, comprising:
The device is
A heating element in thermal contact with the liquid, the heating element configured to supply a known amount of heat to the flowing liquid for a known period of time;
A temperature sensor configured to measure an instantaneous temperature of the heating element;
A control system with a processor and memory,
With
The method
a) operating the heating element to supply the known amount of heat starting at time t1 and ending at time t2;
b) obtaining a data point set representing the temperature rise curve by measuring the temperature of the heating element a plurality of times;
c) recalling a calibration table, graph, or mathematical relationship for the known heat quantity from memory;
d) determining from the calibration table, graph, or mathematical relationship the value of the volumetric flow rate corresponding to the temperature rise curve;
Have
The measurement of the temperature change of the heating element, wherein the carried out several times in the previous and t2 after time t1.

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